1. Field of the Invention
The invention relates to supporting disks for a surface grinding wheel and to a surface grinding wheel comprising a supporting disk.
2. Background Art
Surface grinding wheels comprise a supporting disk and abrasive laminas mounted thereon. The abrasive laminas, which deliver stock removal upon operation, customarily comprise commercial abrasives on a cotton or polyester substrate. As a rule, the abrasive laminas are being fixed on the supporting disk by epoxide resin adhesive. The supporting disk serves for rotating the abrasive laminas and for the pressure necessary for the grinding job to be transmitted by the operator from the driving motor to the abrasive laminas and, consequently, to the subject that is to be machined. Consequently, the supporting disk is only of indirect importance for the result of the grinding job. Another important function of the supporting disk resides in ensuring the necessary safeguard against centrifugal fracture of the surface grinding wheel. Surface grinding wheels are regularly operated at a circumferential speed ranging from 50 m/s to 80 m/s. The considerable mechanical stresses that occur in the supporting disk in this case demand for the use of high-strength material.
It is known from DE 200 05 548 U1 and DE 299 14 325 U1 to make the supporting disk of metal.
DE 298 05 508 U1 further teaches to manufacture a supporting disk for a surface grinding wheel from metal and to provide the outer edge thereof with a plastic material protective arrangement.
It is known from DE 299 10 931 U1 to manufacture a supporting disk for a surface grinding wheel from synthetic resin which is at least partially reinforced by natural fibers.
It is further known to embody supporting disks as glass-fiber reinforced phenolic resin bodies. The production costs are very high in particular when a supporting disk of this type includes a plurality of textile-glass fabrics. More than five and even more than twelve layers of textile-glass fabrics are used as a safeguard against centrifugal fracture.
In particular the flexural strength of the supporting disks is of decisive importance as a safeguard of the tools against centrifugal fracture. When loaded by centrifugal forces, the supporting disk sags as a result of the weight of the abrasive laminas that bears on it, which strongly loads the adhesive mechanically, terminating in the laminas being torn off.
In order to obtain the required flexural strength of the supporting disk, a sufficiently great number of glass fabrics must be selected, which is the present level of knowledge. The necessary number of fabric layers depends on the total weight of the abrasive laminas that are mounted on the supporting disk. The number of abrasive laminas is also directly proportional to the lifetime of the tool. Therefore, tools that have a long lifetime must com-comprise a plurality of fabric layers, for example twelve layers, so as to comply with safety requirements.
It is an object of the invention to embody a supporting disk for a surface grinding wheel in such a way that the supporting disk can be manufactured at a low cost while keeping its highly protective properties of safeguard against centrifugal fracture and to embody a surface grinding wheel that comprises a supporting disk of this type.
This object is attained in a supporting disk for a surface grinding wheel, consisting of a glass-fiber reinforced phenolic resin body, which includes an upper covering layer of a textile glass fabric; an intermediate layer of a fiber fleece; and a lower covering layer of a textile glass fabric. According to the invention, a comparatively expensive textile glass fabric is utilized only in the upper and lower covering layer, whereas a simple intermediate layer in the form of a fiber fleece is used as a filler between these two covering layers. When the supporting disk is loaded during grinding operation, mechanical stresses occur in addition to the strain due to centrifugal force as a result of the supporting disk sagging in the direction of its axis. The greatest bending stresses occur upon loading of the surface areas, while the intermediate area remains almost stress-free when loaded by bending. The coverings of textile glass fabric have a higher loading capacity than the fiber-mat intermediate layer. As opposed to the prior art number of five layers or more, the supporting disk according to the invention only comprises three layers, of which only the two exterior coverings consist of comparatively costly fabrics or layers while the intermediate layer consists of a comparatively low-cost fiber fleece as a filler. The job of the intermediate layer primarily resides in producing as great a distance as possible between the two coverings that possess by far greater tensile strength than the intermediate layer. As a rule, the intermediate layer is thicker than the covering layers.
Generally, the design of the surface grinding disk that is manufactured using a supporting disk of this type is conventional.
Further advantages, features and details of the invention will become apparent from the ensuing description of exemplary embodiments, taken in conjunction with the drawing.